A close encounter

"I have something nice to post in our blog," said my colleague Cesare Capararo from the console. What he had to say made me put the certification plan I was working on down and walk over to the office of satellite experts Jaap Herrman, Michael Kirschner and Kay Müller – a very special rendezvous will occur in space on Friday 28 March 2014.

At 10:47 UTC, GRACE 1 (Gravity Recovery And Climate Experiment) will fly past the International Space Station (ISS). But they won't come that close to each other; not in the romantic sense, of course, as GRACE 1 already has a partner, GRACE 2, which flies 240 kilometres ahead. They are better known as Tom and Jerry. Also in the physical sense, they will not get that close together. The US space agency NASA strictly monitors who or what could be 'flirting' with the ISS. In case of doubt, its trajectory is changed – this sounds more dramatic than it actually is. A bit of acceleration at a carefully chosen point on its orbit will change the course of the ISS to avoid a collision.

In the vastness of space, it is serendipitous that two spacecraft, monitored by the German Space Operations Centre (GSOC) in Oberpfaffenhofen, come so close to each other; NASA has estimated the minimum distance to be less than two kilometres. It is quite peculiar that our in-house expertise equally covers satellites and human spaceflight, but even more so that we are monitoring and analysing the exact same event from two different control rooms that are side by side but rarely have any points of contact.

Last Friday, I made my way to the flight director console earlier than usual; Kay Müller of the GRACE project was there. We were told that no evasive manoeuvres have been planned for the ISS. The measurements and analyses performed throughout the night have shown that the orbits are well determined and any uncertainties are barely measurable. Since there will be no changes, the tête-à-tête will occur at a distance of about two kilometres. We, however, will likely have a 'close encounter' for coffee with our GRACE colleagues after 10:47 UTC…

Image 1: Photomontage showing the twin GRACE satellites, known as 'Tom and Jerry', with the International Space Station. Credit: DLR CC-BY (3.0)

Image 2: The telemetry system SATMON displays the intersecting paths of the space vehicles on the console. Credit: Chris Peat, heavens-above.com